1. Field of the Technology
The invention relates in general to digital channel changing, or zapping, and more particularly, to a system and method for fast digital channel changing.
2. Background of the Technology
The digitatization of Television (TV) broadcast improves TV picture quality greatly, however, it causes a slowdown of channel changing.
This slow changing of digital channels involves the method used for digital video data compression. For example, Internet Protocol Television or Interactive Personal Television (IPTV) and Digital Television (DTV) generally apply a compression protocol, such as Moving Picture Experts Group Compression Standard Version 2(MPEG-2), H.264, Video-Codec 1(VC-1), or Audio Video coding Standard (AVS). The digital video data is transmitted in a series of frames, which includes intra frames (I-frames), predictive frames (P-frames) and bidirectional frames (B-frames). I-frame, also called ‘key’ frame, is an independent frame that may be decoded without reference to other video frames. P-frame is a predictive video frame. P-frame provides information about the occurred change compared to the previous I-frame. B-frame is a bidirectional frame. B-frame contains information of the change that occurred between the I-frame before and after it. B-frame and P-frame are dependent frames that are decoded with reference to one or more other video frames, such as I-frames.
Consecutive frames are displayed very near to each other in time. For example, in Phase Alternating Line (PAL) systems, the frame interval of the frames is 0.04 seconds, and most of the time, the consecutive frames are visually almost the same with little differences. P-frames and B-frames are more efficient than I-frames because they only encode the differences between frames. For this reason, the Broadcast Television (BTV) system uses less I-frames and more P-frames and B-frames to get a higher compression rate. The interval between I-frames is about 0.5 seconds and the frames may be in a sequence, such as IPPPPPPPPPPPI or IBBPBBPBBPBBPI. Because there are more P frames and B-frames than I-frames in data transmission, users have a high likelihood of changing channel of meeting P-frames or B-frames. Because P-frames or B-frames need to be decoded depending on previous I-frames, the users would have to discard the received P-frames or B-frames until an I-frame is received. This is the reason for the slow changing of digital channel.
One way of improving channel changing speed is to be accomplished by a storage device that retains broadcast video data for multiple channels, a video data extractor that accesses the retained broadcast video data and retrieves an intra frame (I-frame) of broadcast video data that is in the past for a requested channel; and a video data distributor that transmits the retrieved intra frame (I-frame) of broadcast video data.
The exemplary method is given as: detecting a channel change request that indicates a requested channel, the requested channel corresponding to a multicast group; and transmitting a retained intra frame for the requested channel as a unicast communication, thus makes the channel changing fast.
To change digital channel fast, the method should be accomplished with a storage device, a video data extractor, a video data distributor, etc., and these devices add cost to the broadcast video data service. At the same time, the unicast communication means every user would occupy the network bandwidth resources, server resources, or other resources, thus loses the benefit of multicast transmitted TV. The more users change channels, the more resources are occupied and wasted. Besides, the storage devices generally are fragile and in the complex procedures are easier to cause the changing failure.
Another way to solve digital channel changing proposes a method to reduce the delay by encoding a video sequence in two bitstreams of different spatial (or spatial and temporal). This contribution suggests encoding video in two layers, for example, a base layer and an enhancement layer, different in spatial resolution, wherein the base layer is a channel with low resolution and low bitrate and the enhancement layer is a normal channel with full resolution. The channel changing procedure requires to change to the base layer and then the enhancement layer of the channel, and to encode the base layer with, so more often Intra refreshing to reduce zapping delay
The given method should apply two channels, which makes the cost of the encoder and the backbone network resource higher, and there is still appreciable degrade of video quality in digital channel changing.
These two ways in the conventional art may solve the problems of slowly channel changing in some extent, but they still have other shortcomings as stated above. Therefore, there is a need for a system and method for changing the channel fast.
Therefore, there is a need for a method and system to make the channel changing quickly.